730 



THE MICROSCOPE. 



Indurated Sandstone, Howth. 



Indurated Sandstone, Bromsgrove. 



Gibraltar rock. 



Granite, various localities. No. 160. 



Hornblend Schist. 



Labrador Spar. 



Norway Eock. 



Quartz Rock, various. No. 159. 



,, in Bog Iron Oro. 



Quartzite, Mont Blanc. 

 Sandstone, Plate VIII. No. 158. 

 Satin Spar. 



Selenites, various colours. 

 Tin Ore, with Tourmalin. 



VEGETABLE SUBSTANCES. 



CUTICLE of Leaf of Correa Cardinal!*. 



,, Dentzia scabra. 



PI. VIII. No. 173. 



Elaiagnus. 



,, ,, Onosma taurica. 



Equisetum. No. 174. 

 Fibro cells from orchM. No. 1C9. 



,, Oucidium bicallosum. 

 Scalariform vessels from Fern. 

 Scyllium. No. 177. 

 SILICIOUS CUTICLES. Various. 

 Starch. Various. No. 167. 



Very interesting results will be obtained by combining 

 two or more chemical salts. Mr. Davies 1 succeeded ia 

 forming numerous beautiful double salts in the following 

 manner. To a nearly saturated solution of the sul- 

 phate of copper, add a drop of a solution of the sulphate 

 of magnesia, on the glass-slide, and dry quickly. To effect 

 this, heat the slide so as to fuse the salts in its water of 

 crystallisation, and there remains an amorphous film on 

 the hot glass. Put the slide aside and allow it to cool 

 slowly ; it will gradually absorb a certain amount of 

 moisture from the air, and begin to throw out crystals. 

 If now placed under the microscope, numerous points 

 will be seen to start out here and there. The starting 

 points may be produced at pleasure by touching the 

 film with a fine needle point, so as to admit of a slight 

 amount of moisture being absorbed by the mass of 

 salt. Development is at once suspended by applying 

 gentle heat ; cover the specimen with balsam and thin 

 glass. The balsam should completely cover the edges 

 of the thin glass circle, otherwise moisture will probably 

 insinuate itself, and destroy the form of the crystals. 



Mr. Thomas succeeded in crystallising " the salts of 

 the magnetic metals " at very high temperatures, which 

 gave interesting results, and produced curious forms of 

 crystals. Plate VIII. JSTo. 163 are representations of 

 crystals of sulphate of iron and cobalt, No. 165, of nickej 

 and potash, obtained in the following manner : To form 

 the sulphate of iron crystal, add to a concentrated solution 

 of iron a small quantity of sugar, to prevent oxidation. 

 Put a drop of the solution on a glass slide, and drive out the 



(I) Quart. Journ. Micros. Scien., rol. ii. p. 128. 1862. 



